This invention relates to a method for the manufacture of poly(etherimide)s. More particularly, it relates to a method for the preparation of dianhydrides that can facilitate the manufacture of poly(etherimide)s without an intermediate nitration step.
Polyetherimides are high heat engineering plastics having a variety of uses. As disclosed in U.S. Pat. Nos. 4,417,044; 4,599,429; 4,902,809; and 4,921,970, the present commercial process for the synthesis of polyetherimides requires nitration of N-methylphthalimide to yield 4-nitro-N-methylphthalimide. Nitration often results in the formation of byproducts, which must be separated. In the next step of the process, 4-nitro-N-methylphthalimide is treated with the disodium salt of a dihydroxy compound, usually a bis(phenol) such as bisphenol A, to yield a bisimide (I) having the following general structure: 
Suitable displacement reactions are disclosed in U.S. Pat. No. 4,257,953. Displacement is also disclosed in U.S. Pat. Nos. 5,132,423 and 5,872,294. Bisimide (I) is then reacted with a phthalic anhydride in an exchange reaction as disclosed in U.S. Pat. Nos. 4,318,857, 4,329,291, 4,329,292, 4,329,496, and 4,340,545 to yield the dianhydride (II): 
Reaction of dianhydride (II) with a diamine results in polymerization to a poly (etherimide). Methods which improve or even eliminate any of the preceding steps would result in an improved synthesis of poly(etherimide)s.
A new method for the synthesis of poly(etherimide)s which eliminates the nitration step comprises synthesis and reaction of a substituted N-alkylphthalimide (III) 
with the disodium salt of a dihydroxy compound such as a bis(phenol) to yield the bis (imide) (IV) 
Bis(imide) (IV) is then subjected to transimidation to yield the dianhydride (V) 
Transimidation is effected in the presence of a substituted phthalic anhydride, which yields a substituted N-alkylphthalimide that corresponds to the substituted phthalic anhydride as a by-product. By-product substituted N-alkylphthalimide may then be recycled for use in the formation bisimide (IV).
In another embodiment, transimidation is effected in the presence of 4-substituted tetrahydrophthalic anhydride, which yields a 4-substituted N-alkyltetrahydrophthalimide as a by-product. The by-product 4-substituted N-alkyltetrahydrophthalimide may be converted by aromatization to a 4-substituted N-alkylphthalimide, which may be used in the formation of bis(imide) (IV).
Finally, the reaction of dianhydride (V) with a diamine (VI) having the structure
H2Nxe2x80x94Rxe2x80x94NH2xe2x80x83xe2x80x83(VI)
yields poly(etherimide)s. This route obviates the need for the intermediate nitration step required by the prior art synthesis.
A convenient route for the manufacture of poly(etherimide)s comprises synthesis and reaction of a substituted N-alkylphthalimide (III): 
wherein the alkyl group is a branched or straight chain alkyl group having from one to about 18 carbons. Preferably, the alkyl group is a methyl group. The substituent (X) is a nitro, chloro, bromo, or fluoro in the 3- or 4- position. Substituted N-alkylphthalimides may be obtained by the treatment of the corresponding substituted phthalic anhydride with a primary amine having the formula H2N-alkyl via a melt reaction, for example by contact of a gaseous primary amine such as methylamine with molten 4-halophthalic anhydride. Halophthalic anhydrides may be obtained by aromatization of the corresponding halotetrahydrophthalic anhydrides as disclosed in U.S. Pat. Nos. 5,233,054, 5,003,088, 5,059,697 and 4,978,760. Halophthalic anhydrides may also be obtained by the aromatization of the corresponding halotetrahydophthalic anhydrides in the presence of a catalyst such as a transition metal oxide. Nitro substituted phthalic anhydrides may be obtained by the nitration of phthalic anhydrides as taught in U.S. Pat. No. 5,155,234.
Displacement of the substituent of the substituted N-alkylphthalimide (III) may be effected by treatment with the disodium salt of a dihydroxy compound having the formula (VII)
HOxe2x80x94Sxe2x80x94OH (VII)
to yield the bis(imide) (IV) 
wherein S is a divalent radical, for example a straight or branched chain alkylene group having from about 2 to about 20 carbon atoms; a cycloalkylene group having from about 3 to about 20 carbon atoms; or an arylene group having from 6 to about 20 carbon atoms, and halogenated derivatives thereof. The alkylene, cycloalkylene, and arylene groups may be further substituted with alkyl, halogenated alkyl, fluoro, alkoxy, nitro, phenyl, phenoxy, aryl or other groups, provided that such substitutions do not interfere with synthesis or reaction. The displacement reaction between the dihydroxy compound and the substituted N-alkylphthalimide may be conducted in an inert solvent such as toluene, xylene, chlorobenzene or dichlorobenzene in the presence of a phase transfer catalyst such as hexaethylguanidinium chloride at a temperature in the range of about 110 to about 180xc2x0 C. as taught in U.S. Pat. No. 5,132,423, which is incorporated by reference herein. Displacement may also occur in the melt phase with the substituted N-alkyphthalimide.
A particularly preferred dihydroxy compound is bis(phenol) (VIII) 
wherein T is a single bond linking the two aryl groups, or a divalent radical, for example a straight or branched chain alkylene group having from one to about 20 carbon atoms; a cycloalkylene group having from about 3 to about 20 carbon atoms; or an arylene group having from 6 to about 20 carbon atoms, and halogenated derivatives thereof. The alkylene, cycloalkylene, and arylene groups may be further substituted alkyl, halogenated alkyl, fluoro, alkoxy, nitro, phenyl, phenoxy, aryl or other groups, provided that such substitutions do not interfere with synthesis or reaction. T further includes divalent functional groups such as sulfide, carbonyl, sulfoxide, and ether and divalent radicals of formula (XV) 
Illustrative examples of bis(phenol)s of formula (VIII) include 2,2-bis[4-hydroxyphenyl]propane; 4,4xe2x80x2-bis(4-hydroxyphenyl)diphenyl ether; 4,4xe2x80x2-bis(4-phenoxy)diphenyl sulfide; 4,4xe2x80x2-bis(4-hydroxyphenyl)benzophenone; 4,4xe2x80x2-bis(4-hydroxyphenyl)diphenyl sulfone; 2,2-bis[4-(3-hydroxyphenyl)phenyl]propane; 4,4xe2x80x2-bis(3-hydroxyphenyl)diphenyl ether; 4,4xe2x80x2-bis(3-hydroxyphenyl)diphenyl sulfide; 4,4xe2x80x2-bis(3-hydroxyphenyl)benzophenone; 4,4xe2x80x2-bis(3-hydroxyphenyl)diphenyl sulfone; 4-(3-hydroxyphenyl)-4xe2x80x2-(4-hydroxyphenyl)diphenyl-2,2-propane; 4-(3-hydroxyphenyl)-4xe2x80x2-(4-hydroxyphenyl)diphenyl ether; 4-(3-hydroxyphenyl)-4xe2x80x2-(4-hydroxyphenyl)diphenyl sulfide; 4-(3-hydroxyphenyl)-4xe2x80x2-(4-hydroxyphenyl) benzophenone, and 4-(hydroxyphenyl)-4xe2x80x2-(4-hydroxyphenyl)diphenyl sulfone dianhydride, as well as various mixtures thereof. These and other bis(phenol)s and dihydroxy compounds are described in U.S. Pat. Nos. 3,972,902 and 4,455,410.
Bis(imide) (IV) is treated with a substituted phthalic anhydride (IX) 
via transimidation to yield dianhydride (V) 
wherein S is as described above. Useful substituted phthalic anhydrides have a nitro, chloro, bromo, or fluoro group in the 3 or 4 position although chloro and bromo substituents are preferred. Also preferred are mixtures of structural isomers, for example a mixture comprising 3-halophthalic anhydride and 4-halophthalic anhydride. Surprisingly, reaction conditions may be adjusted so as to minimize the formation of the N-alkylamino-N-alkylphthalimide (from the displacement of the halo group with alkylamine), a highly colored by-product which can impart an undesirable color to the product dianhydride. Preferably, the YI of the product is less than about 25, and more preferably less than about 15 as measured by the UV spectrum of the product.
A desired by-product of this reaction is substituted N-alkylphthalimide (III), which may be isolated and used for reaction with a dihydroxy compound (VII) as described above.
In an alternative embodiment, transimidization of bis(imide) (IV) is effected in the presence of 4-substituted tetrahydrophthalic anhydride (X) 
Useful substituents are nitro, chloro, fluoro and bromo. Chloro and bromo substituents are preferred. 4-substituted tetrahydrophthalic anhydride (X) is available from the Diels-Alder condensation of the dienophile maleic anhydride with the 2-substituted-1,3-butadiene. Conditions for this reaction are known in the chemical literature.
The by-product of this transimidization is a 4-substituted N-alkyltetrahydrophthalimide (XI) 
4-substituted N-alkyltetrahydrophthalimide (XI) may be converted by aromatization to 4-substituted N-alkylphthalimide, which can be used in the displacement reaction with the dihydroxy compound as described above. Aromatization may be achieved by any method known in the art such as those taught by U.S. Pat. Nos. 5,233,054, 5,003,088, 5,059,697, and 4,978,760. Alternately, aromatization can be achieved in the presence of a transition metal oxide catalyst such as vanadium oxide;(V2O5) at a temperature in the range of about 250xc2x0 C. to about 270xc2x0 C.
Transimidization with either substituted phthalic anhydrides (IX) or 4-substituted tetrahydrophthalic anhydride (X) may be conducted in an inert solvent such as water in the presence of a base such as triethylamine at a temperature in the range from about 150 to about 250xc2x0 C., and preferably in the range from about 160 to about 180xc2x0 C. For example, transimidation is effected by reaction of bis(imide) (IV) with a 6-7 fold molar excess of substituted phthalic anhydride (IX) or 4-substituted tetrahydrophthalic anhydride (X) in water in the presence of at least one mole of base, e.g., triethylamine, per mole of anhydride at about 170xc2x0 C. for about one to about 1 to 2 hours.
Preferably, the aqueous reaction mixture is then continuously extracted in a packed column with an organic solvent, e.g., toluene, containing a base such as triethylamine to remove unconverted bis(imide) (IV) and the formed substituted N-alkylphthalimide (III) or 4-substituted N-alkyltetrahydrophthalimide (XI). Transimidation may continue within the column. The aqueous eluent from the column contains the tetraacid of dianhydride (V) and substituted phthalic diacid, both present as base conjugated salts. The aqueous solution is fed to a flash distillation vessel whereby a majority of the water and some of the base is removed. The bottoms from this vessel are fed to a wiped film evaporator under vacuum, where the base conjugated salts crack to liberate base with concomitant ring closure of diacids and tetraacids to anhydride and dianhydride. Water, base, and substituted phthalic anhydride or 4-substituted tetrahydrophthalic anhydride are taken overhead. The dianhydride is isolated as a molten liquid from the bottom of the wiped film evaporator. The base, water, and the substituted phthalic anhydride or 4-substituted tetrahydrophthalic anhydride from the flash vessel and from the wiped film evaporator are recycled back to the exchange reactor.
Preferably, the organic eluent from the extraction process is fed to a flash vessel wherein the solvent and the base are removed from the heavier organics. These overheads are recycled back to the bottom of the exchange column. The bottom from this flash vessel is fed to another flash vessel where substituted N-alkylphthalimide, when present, (or 4-substituted N-alkyltetrahydrophthalimide) is (III) taken over head. Substituted N-alkylphthalimide may then be purified before being reused in the displacement reaction. When 4-substituted N-alkyltetrahydrophthalimide is present it must first be converted by aromatization to 4-substituted N-alkyl phthalimide then used in the displacement reaction. The bottom of the flash vessel primarily contains primarily recycled bis(imide) (IV), imide-anhydride (bisimide wherein only one of the imides has been converted to an anhydride), and some substituted N-alkylphthalimide (III) or 4-substituted N-alkyl phthalimide. These may be cycled back to the exchange reactor.
Dianhydride (V) may then be reacted with diamine (VI) to yield poly(etherimide)s. Diamine (VI) has the structure
H2Nxe2x80x94Rxe2x80x94NH2xe2x80x83xe2x80x83(VI)
wherein R in formula (VI) includes but is not limited to substituted or unsubstituted divalent organic radicals such as: (a) aromatic hydrocarbon radicals having about 6 to about 20 carbon atoms and halogenated derivatives thereof; (b) straight or branched chain alkylene radicals having about 2 to about 20 carbon atoms; (c) cycloalkylene radicals having about 3 to about 20 carbon atoms, or (d) divalent radicals of the general formula (XII) 
wherein Q includes but is not limited to divalent a divalent moiety selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94C(O)xe2x80x94, xe2x80x94SO2xe2x80x94, CyH2kxe2x80x94 (y being an integer from 1 to 5), and halogenated derivatives thereof, including perfluoroalkylene groups.
Any diamino compound may be employed. Examples of suitable compounds are ethylenediamine, propylenediamine, trimethylenediamine, diethylenetriamine, triethylenetetramine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, 1,12-dodecanediamine, 1,18-octadecanediamine, 3-methylheptamethylenediamine, 4,4-dimethylheptamethylenediamine, 4-methylnonamethylenediamine, 5-methylnonamethylenediamine, 2,5-dimethylhexamethylenediamine, 2,5-dimethylheptamethylenediamine, 2,2-dimethylpropylenediamine, N-methyl-bis (3-aminopropyl) amine, 3-methoxyhexamethylenediamine, 1,2-bis(3-aminopropoxy) ethane, bis(3-aminopropyl) sulfide, 1,4-cyclohexanediamine, bis-(4-aminocyclohexyl) methane, m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene, 2,6-diaminotoluene, m-xylylenediamine, p-xylylenediamine, 2-methyl-4,6-diethyl-1,3-phenylene-diamine, 5-methyl-4,6-diethyl-1,3-phenylene-diamine, benzidine, 3,3xe2x80x2-dimethylbenzidine, 3,3xe2x80x2-dimethoxybenzidine, 1,5-diaminonaphthalene, bis(4-aminophenyl) methane, bis(2-chloro-4-amino-3,5-diethylphenyl) methane, bis(4-aminophenyl) propane, 2,4-bis(b-amino-t-butyl) toluene, bis(p-b-amino-t-butylphenyl) ether, bis(p-b-methyl-o-aminophenyl) benzene, bis(p-b-methyl-o-aminopentyl) benzene, 1,3-diamino-4-isopropylbenzene, bis(4-aminophenyl) sulfide, bis(4-aminophenyl) sulfone, bis(4-aminophenyl) ether and 1,3-bis(3-aminopropyl) tetramethyldisiloxane. Mixtures of these compounds may also be present. The preferred diamino compounds are aromatic diamines, especially m- and p-phenylenediamine and mixtures thereof.
All patents cited herein are incorporated by reference.